High-power solid-state radio frequency power amplifiers (RFPAs) are used in a wide variety of applications including, for example, wireless communications, jamming, imaging, radar, and RF heating.
To achieve high gain, high-power solid-state RFPAs are often designed in multiple stages. FIG. 1 is a simplified drawing of a multi-stage high-power solid-state RFPA 100. The high-power solid-state RFPA 100 comprises an input stage 102, a driver stage 104, and a high-power output stage 106. The primary purpose of the high-power output stage 106 is to convert DC energy from its DC power supply to RF energy and thereby produce RF power that is significantly higher than the RF power applied to its input.
The efficiency of a multi-stage RFPA is heavily dependent upon the high-power output stage's ability to achieve fast slew rates. Unfortunately, the transistors used in the high-power output stages of multi-stage RFPAs must be large and therefore unavoidably have large input capacitances. The large input capacitances make fast slew rates very difficult to realize. The high-power output stage is the stage in the RFPA that consumes the majority of power. Consequently, in most applications, finding ways to make the high-power output stage operate as efficiently as possible is paramount. Since the driver stage controls the operation of the high-power output stage, how the driver stage is designed substantially affects how efficient the high-power output stage can possibly be. For this reason, the driver stage deserves special attention.